1. Field of the Invention
The present invention relates to a barrel provided as an element of a zoom lens and having one or more than one cam groove on one of the outer and inner peripheral surfaces of the barrel and a helicoid on the other peripheral surface of the barrel.
2. Description of the Related Art
In order to design a compact zoom lens and/or reduce the number of elements of a zoom lens, it is often the case that more than one function is given to an element of the zoom lens. For instance, the zoom lens is provided therein with a barrel having one or more than one cam groove on one of the outer and inner peripheral surfaces of the barrel and a helicoid (helicoidal threaded portion) on the other peripheral surface of the barrel. However, the wall thickness (i.e., the radial thickness of the cylindrical wall) of such a conventional barrel is generally large to maintain a sufficient strength thereof, which makes it difficult to reduce the diameter of the barrel.
The present invention has been made in view of the problem noted above, wherein an object of the present invention is to provide a barrel which can be used as an element of a zoom lens which makes it possible to reduce the diameter of the barrel while maintaining a sufficient strength thereof.
To achieve the object mentioned above, according to an aspect of the present invention, a barrel is provided, including at least one cam groove and a helicoid on one and the other of outer and inner peripheral surfaces of the barrel, respectively; wherein a wall thickness of the barrel corresponds to the sum of a height of teeth of the helicoid and a depth of the cam groove, so that the cam groove forms through-holes in the wall of the barrel where no teeth exist.
With this structure, the barrel can be made small because through-holes are formed on the barrel along the cam groove or grooves therein, while part of the barrel around the cam groove or grooves can be reinforced by the teeth of the helicoid to thereby ensure the strength of the barrel.
Preferably, the teeth of the helicoid extend in an inclination direction different to an inclination direction of the cam groove with respect to an axis of the barrel.
Preferably, the cam groove is formed so that the width thereof gradually decreases in a radial and outward direction of the barrel.
Preferably, a plurality of cam grooves having different profiles are provided on the barrel.
Preferably, the teeth of the helicoid are formed integral with the barrel.
In an embodiment, the cam groove and the helicoid are formed on the inner peripheral surface of the barrel and the outer peripheral surface of the barrel, respectively.
Preferably, the barrel is provided as an element of a zoom lens.
According to another aspect of the present invention, a barrel is provided, including at least one cam and a helicoid on one and the other of outer and inner peripheral surfaces of the barrel, respectively; wherein the cam is formed as a cam slot which forms through-holes in the barrel in a radial direction of the barrel, and wherein teeth of the helicoid are connected to the cam slot so as to partly cover an outer opening of the cam slot.
According to another aspect of the present invention a barrel is provided, including at least one cam groove formed on one of outer and inner peripheral surfaces of the barrel; and a helicoid formed on the other of the outer and inner peripheral surfaces of the barrel, wherein teeth of the helicoid extend in an inclination direction different to that of the cam groove with respect to an axis of the barrel, and wherein the cam groove is formed so as to form through-holes in the barrel where the teeth of the helicoid do not overlap the cam groove.
According to another aspect of the present invention, a zoom lens is provided, including an outer barrel provided on an inner peripheral surface thereof with a female helicoid; an inner barrel provided on an outer peripheral surface thereof with a male helicoid, wherein a feed operation is carried out in accordance with the engagement of the male and female helicoids; and at least one cam groove formed on an inner peripheral surface of the inner barrel, wherein teeth of the male helicoid extend in an inclination direction different to an inclination direction of the cam groove with respect to an axis of the barrel, and the cam groove is formed so as to form through-holes in the barrel where teeth of the male helicoid do not overlap the cam groove.
The present disclosure relates to subject matter contained in Japanese Patent Application No.11-299846 (filed on Oct. 21, 1999) which is expressly incorporated herein by reference in its entirety.